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Getting there more safely INNOVATION INSIGHTS with Richard Langley It’s all physics. How things work, that is. You’ve heard me say that before in this column, but I suppose I’m a little biased (or realistic) as my first degree is in physics — applied physics, to be more precise. Mind you, some chemists might disagree that it’s all down to physics. But as Sheldon Cooper in the popular American TV sitcom The Big Bang Theory stated in a radio interview with real science journalist Ira Flatow following his apparent discovery of the first stable super-heavy element, “Yes, yes, I’d be a physicist with a Nobel in chemistry. Everyone laugh at the circus freak. You know, I don’t need to sit here and take this, Flatow. It is because of bullies like you, every day more and more Americans are making the switch to television.” But in all seriousness, it really was physicists who first explained the physical phenomena associated with a range of technologies that had to be understood before global navigation satellite systems could become a reality. From orbital mechanics, to relativity theory, to semiconductors, to transatmospheric propagation of radio signals, to atomic clocks, the fundamental understanding of how these worked was provided by physicists. This was particularly true for atomic clocks. An atomic clock, like any clock, consists of two basic components: a resonator or oscillator and a counter. The oscillator generates a stable frequency, whose cycles are counted, converted to units of seconds, minutes, hours and perhaps days, and continuously displayed. This is the case whether we are describing a wristwatch with a quartz crystal oscillator or an atomic clock whose oscillator is made up of atoms undergoing quantum energy transitions. A crystal oscillator is stimulated to vibrate at its design frequency and thereby generate a fluctuating electrical current with that frequency. The atomic oscillator works thanks to the principles of quantum physics. Atoms have energies, but the energies are quantized, meaning that only specific energy levels are possible. An atom may exist at a particular energy level and spontaneously transition to a lower energy level and in so doing emit electromagnetic radiation (such as radio waves or light) of a specific frequency equal to the change in energy divided by a fundamental physical constant called Planck’s constant, named after Max Planck, who introduced it in 1900. The atom can be stimulated to return to the higher energy level by exposing it to radiation of that same exact frequency. A practical atomic oscillator can be constructed by confining a collection of atoms in an enclosure and bathing them in electromagnetic radiation from a tunable generator. By automatically tuning the frequency of the generator to maximize the number of stimulated atoms through a feedback loop, a very pure and constant frequency will result. The first clocks based on an energy transition of the cesium atom were developed in the mid-1950s. Later on, clocks based on energy transitions of the rubidium and hydrogen atoms were developed. By the 1960s, commercial rack-mountable cesium and rubidium clocks became available. But a need existed for miniaturized atomic clocks that could be easily embedded in equipment requiring a very stable frequency source. Funded in part by the Defense Advanced Research Projects Agency, the first chip-scale atomic clock was demonstrated by physicists in 2004, and by 2011, a chip-scale atomic clock based on a cesium atom transition became commercially available. In this month’s column, we look at how chip-scale atomic clocks can help us navigate more safely by allowing a GNSS receiver to position itself more accurately even with only three satellites in view, and to protect itself by being able to detect a sophisticated spoofing attempt. Physics — isn’t it wonderful! GNSS positioning and navigation are based on one-way range measurements. Synchronization of the receiver and satellite timescales is carried out with respect to a third time scale of higher stability, such as GNSS system time, by introducing so-called clock errors. To account for the time and frequency offsets of the satellites, the user can obtain appropriate corrections from the broadcast navigation message in real time. In post-processing, more accurate corrections are provided by various products of the International GNSS Service (IGS). Due to the generally poor accuracy and limited long-term frequency stability of a quartz oscillator built into a GNSS receiver, the receiver clock error has to be estimated epoch-by-epoch. This is the typical case for single-point positioning (SPP) based on code (pseudorange) observations only. This comes with certain drawbacks: The up-coordinate is determined two to three times less precisely than the horizontal coordinates, Higher dilution of precision values are obtained than in the hypothetical case of trilateration, High correlations of up to 99 percent between the receiver’s up-coordinate and clock error persist, and At least four satellites are necessary for positioning. Especially in the case of kinematic positioning, this situation can be significantly improved by using a more stable (atomic) clock for the receiver and introducing the information about its frequency stability into the estimation process. This approach is called receiver clock modeling (RCM), and basically requires that the integrated clock noise is smaller than the receiver noise during the modeling interval. Besides SPP, this method can also be applied in a common-clock setup in relative positioning using single-differenced observations (which, by their nature, contain more information) instead of typically used double-differenced observations, or precise point positioning. The recent development of chip-scale atomic clocks (CSACs) offers the required frequency stability and accuracy, and opens up the possibility of using atomic clocks in real kinematic GNSS applications without any severe restrictions regarding power supply or environmental influences on the clocks. When connecting one of these clocks to a GNSS receiver, replacing or steering the internal oscillator accordingly, and modeling its behavior in a physically meaningful way instead of epoch-wise estimation, the navigation performance can be improved distinctly. The receiver clock parameter absorbs signal delays common to all simultaneous line-of-sight signals whether these delays represent the physical clock or any other common delay. Thus, it is especially vulnerable to delays caused by jammers or spoofers. If the clock behavior is predictable, information about jamming or spoofing can be retrieved, and thus the integrity of the positioning solution can be improved. Chip-Scale Atomic Clocks For our test purposes, we used two different commercially available CSACs, dubbed CSAC A and CSAC B. To gain knowledge about their frequency stabilities, we compared them against an active hydrogen maser at the Physikalisch-Technische Bundesanstalt (PTB), Germany’s official metrology institute. We analyzed the raw fractional phase measurements and computed individual Allan variances for our devices. The resulting frequency stabilities are shown in FIGURE 1. Clock Model Basically, a clock is an oscillator generating a sinusoidal signal with a given nominal frequency coupled with a frequency counter. The deviation of the signal’s nominal frequency with respect to a reference time scale can be described by a frequency offset and drift plus random frequency fluctuations. In the time domain, the resulting clock error δt, that is, the difference between nominal time t and the time read simultaneously on the clock, can be approximated by the following equation: (1)   with systematic time offset b0, frequency offset b1, frequency drift b2, and random noise x(t,t0). Thus, the main (deterministic) part of a clock model can be described by a quadratic polynomial. The more interesting characteristics of a clock are contained in the underlying noise processes. The time-dependent Allan deviation (ADEV) enables the determination of a modeling or predicting interval τp over which receiver clock modeling is physically meaningful; that is, the integrated clock noise x(t,t0) is smaller than GNSS receiver noise: (2)   The noise σrx of a typical commercial GNSS receiver can be assessed to approximately one percent of the chip or wavelength of the signal in use, such as 3 meters, 0.3 meter, or 2 millimeters for C/A-code, P-code, or L1 carrier-phase observations, respectively. To apply the knowledge gained about the devices’ frequency stabilities, appropriate models for GNSS data analysis should be established. One prerequisite is that the clock noise has to be well below the GNSS receiver noise; that is, the integrated random frequency fluctuations of CSACs cannot be resolved by the GNSS observations in use. We assume typical values for code and ionosphere-free carrier-phase observations from modern geodetic GNSS receivers of 1 meter and 5 millimeters, respectively. Since these observations are phase-based measures, we can model the dominating underlying noise process as white-noise phase modulation (WPM) over time. The corresponding graphs are depicted in FIGURE 1 as dashed lines. The intersection points between these lines and the ADEV curves define maximal time intervals Δt for physically meaningful receiver clock modeling in our case study. Depending on the CSAC in use, RCM is applicable over time intervals of at least ten minutes and up to one hour in C/A-code-based applications, such as SPP. GNSS Applications We have tested and validated our receiver clock modeling approaches for GNSS navigation. Kinematic Experiment We carried out a real kinematic experiment on a cart track in farm fields with an approximately 500 × 800 square meter area with only a few natural obstructions in the form of a tree-lined lane (see FIGURE 2). The basic measurement configuration consisted of four GNSS receivers running the same firmware version connected to a GNSS antenna via an active signal splitter. Three of these receivers were fed by the 10-MHz signals of our CSACs. For comparison purposes, the fourth receiver was driven by its internal quartz oscillator. Each test drive with our motor vehicle lasted approximately 8 to 10 minutes. We recorded GPS and GLONASS data with a sampling interval of one second. (Only GPS-based results are described herein.) That was also the case for our temporary local reference station, which consisted of a GNSS antenna mounted on a tripod and connected to another GNSS receiver. Hence, we were able to generate reference solutions for the vehicle trajectories in relative positioning mode with baselines of up to only some hundred meters, yielding 3D coordinate accuracies below 20 centimeters. The RCM algorithms presented here were implemented in the Institut für Erdmessung GNSS Matlab Toolbox. To compute a typical real-time SPP navigation solution based on GPS C/A-code observations only, broadcast ephemerides were used. Tropospheric and ionospheric signal delays were corrected by the Saastamoinen and Klobuchar models, respectively. [Click on an image to enlarge it.] FIGURE 1. Allan deviations of investigated atomic clocks and GPS ionosphere-free carrier and C/A-code observation noise modeled as white-noise phase modulation (WPM) over time. FIGURE 2. Test track. The yellow ellipse marks a treed lane with signal obstructions. Precision and Accuracy Two of the most important GNSS performance parameters are the precision and accuracy of the coordinate solution. FIGURE 3 shows topocentric coordinate differences with respect to the reference trajectory and clock-error time series of the receiver driven by its internal quartz oscillator, estimated without RCM. This is typical for almost all end users. The (linearly detrended) receiver clock error exhibits values between roughly −100 and +200 nanoseconds, which is typical for a quartz oscillator. The noise of the coordinates is in the range of 20–25 centimeters in the horizontal components and about 50 centimeters in the up-component, respectively. Furthermore, certain coordinate offsets are visible due to remaining systematic effects such as ionospheric delay and orbit errors. We could attribute these effects thanks to repeated analysis runs with different correction models such as precise IGS final orbits or by forming the ionosphere-free linear combination. Hence, the assessment of the accuracy of the results is difficult since it chiefly depends on the applied correction models, and it is less influenced by receiver clock modeling. Without use of RCM, the three receivers connected to the CSACs show similar behavior in the coordinate domain. However, the clock residuals become very small compared to those of the internal oscillator and amount to only a couple of nanoseconds at most. As an example, FIGURE 4 depicts the results for CSAC A. Even over a relatively short period of time of approximately eight minutes, this oscillator shows a significant frequency drift, which we have to account for in RCM. Note that this is also true for the device’s oven-controlled crystal oscillator (OCXO) post-filtered signal. When applying RCM, as expected, no changes in the time series of the north and east coordinates occur, but a strong decrease of the up-coordinate residuals is clearly visible. The noise level is up to 20–30 centimeters. Due to the applied polynomial clock model, the clock residuals are also reduced. Thanks to the increasing number of epochs/observations contributing to the estimation of the clock parameters, the course of these residuals gets smoother over time. Furthermore, spikes in the up-coordinate time series at around minutes five to seven caused by sudden signal obstructions are almost eliminated thanks to RCM. Also, when applying RCM, there are no improvements in the horizontal components, but the scatter of the up-coordinates is decreased in the range of 48 percent (CSAC B) to 58 percent (CSAC A). Our second RCM approach based on an existing extended Kalman filter clock model shows comparable results. The most obvious difference to a sequential least-squares approach is that the spikes in the up-coordinate and clock residual time series at around minutes five to seven are not smoothed as strongly. Reliability and Integrity Reliability and integrity are very important GNSS performance parameters, especially for real-time and safety-of-life critical applications. In general, we distinguish between internal and external reliability, which are both measures for the robustness of the parameter estimation against blunders in the observation data. Thereby, good reliability makes it easier to identify and remove gross errors and outliers in GNSS data analysis. Internal reliability is calculated in terms of so-called minimal detectable biases (MDBs) of the GNSS observations. These values determine lower bounds for gross observation errors so that these can still be detectable. External reliability describes the influence of these MDBs on the parameter estimates. In our experiments, we found reductions in the size of the MDBs of up to 16 percent. As a consequence, the vertical protection level — a measure of integrity — is also improved. Positioning with 3 Satellites Generally, GNSS positioning requires at least four satellites in view to solve the equation system for the four unknowns. This can become a severe restriction in difficult environments such as urban canyons. Taking benefits of an oscillator of high accuracy, with known and predictable frequency stability, enables positioning using only three satellites. This approach enhances GNSS continuity and availability, and is called clock coasting. Thanks to the stability of CSACs, the GNSS observations are corrected by an additional receiver clock term, which is computed from the latest clock-coefficient estimates. To show the effects of this method, we generated two artificial partial satellite outages so that only observations on only three satellites remain. The latter were chosen in such a way that typical situations in an urban canyon were simulated; that is, only satellites with high elevation angles were visible to the receiver. The resulting coordinate and clock time series are depicted in FIGURE 5. When coasting through periods with only three satellites available, the horizontal coordinates become approximately two to three times noisier (1–2 meters). Due to the poor observation geometry, an additional offset of about 1 meter is induced in the north component during the first partial outage. However, the noise of the up-coordinate is only slightly increased in both of the outage periods, although a significant drift is visible during the first one. Most likely, this is because the coefficients used for clock coasting are only based on 60 epochs up until that time. During the second partial outage this drifting behavior vanishes independently of the satellite geometry. Due to the fact that the clock time series are linearly detrended and a linear clock polynomial is applied, the corresponding residuals shown in FIGURE 5 equal zero during the coasting periods. The presented approaches for RCM and clock coasting are applicable in multi-GNSS positioning and timing data analysis, too, where we also have to consider inter-system biases. Thanks to the high temporal stability of these biases, they can be modeled by a polynomial in the same sense as the receiver clock error. [Click on an image to enlarge it.] FIGURE 3. Topocentric coordinate deviations with respect to the reference trajectory and clock errors. The receiver is driven by its internal oscillator. No receiver clock modeling was applied in a sequential least-squares adjustment. Note the different y-axis scales. FIGURE 4. Topocentric coordinate deviations with respect to the reference trajectory and clock errors for a receiver connected to the CSAC A signal. The results without receiver clock modeling are depicted in black and blue. The results applying a quadratic polynomial for clock modeling in a sequential least-squares adjustment are shown in red. FIGURE 5. Topocentric coordinate deviations with respect to the reference trajectory and clock errors. The receiver is connected to CSAC B. The solution is obtained from a sequential least-squares adjustment with clock coasting from minutes one to two and five to seven. Spoofing Detection Jamming and spoofing of GNSS signals have become major threats to GNSS positioning and timing. Although these authentication issues have been well known since the beginnings of GPS, they have become more severe in recent years due to the greatly increased number of applications that rely on (highly) accurate GNSS positioning and timing. Experiment A spoofing attack’s goal is for the signal tracking loops of a target receiver to acquire the spoofing signal, and then pull its navigation solution away from the authentic position. So as not be detected by the target receiver, the common delay of the spoofing signals — which will be absorbed by the receiver’s clock-error estimate — must not deviate significantly from the receiver’s authentic clock error. This means that the injected delay has to be as small as possible so that it cannot be separated from the typical random frequency (and thus time) fluctuations of the oscillator driving the receiver. To simulate a spoofing attack, we set up an experiment consisting of two GNSS receivers, one driven by its internal quartz oscillator, and one connected to CSAC B, both recording the same GNSS signals via a signal splitter. The input signal of the latter comes from an active coaxial switch, which allows us to switch between two different antennas in less than 1 second. Both antennas in our measurement configuration were mounted on tripods. However, one antenna was connected to a commercial GNSS repeater, which generates an additional delay, and its output signals were transmitted via cable to the coaxial switch (see FIGURE 6). When switched to the antenna without the repeater, the receivers recorded authentic signals. When switched to the repeater, they recorded spoofed signals. The location of the repeater antenna ranges from 2 to 25 meters away from the authentic antenna, thereby introducing different delays — in addition to the repeater delay — into the signal processing of the two receivers. We assume that a short delay of about 2 meters (7 nanoseconds) is more difficult for receivers to detect than a delay of about 25 meters (83 nanoseconds). Whenever the signal path is switched from the authentic antenna to the repeater antenna, this should result in a jump in the clock-error time series. Combined with the known frequency stability of the receivers’ oscillators, we can establish a hypothesis test for the significance of such a clock-error jump. For each new location of the repeater antenna, the measurement procedure was the same. We recorded authentic and spoofed data four times alternating for two minutes with a data rate of 1 Hz. FIGURE 6. Measurement configuration of a spoofing detection experiment. Results FIGURES 7 and 8 show the original clock-time offsets for two different locations of the repeater antenna as recorded by the receivers, and the corresponding predicted clock states from the Kalman filter. The jumps in each clock-error time series are more or less clearly visible, especially in the case of the 2-meter distance. For the latter, the hypothesis test of the temperature-controlled crystal oscillator (TCXO) always accepts the alternative in favor of the null hypothesis; that is, from a statistical standpoint, no spoofing attack is detectable. This is because of the small signal delay attributable to the measurement geometry, which cannot be properly separated from random time deviations caused by the TCXO’s low frequency stability. On the contrary, even for this short distance between the spoofing and authentic antennas, every start and end of the four spoofing attacks were detected. As an example, FIGURE 8 shows the results for a larger distance (around 14 meters). In this case, all spoofing attacks can be properly detected by both the TCXO- and the CSAC-controlled receivers. The seven-times-increased distance ensures that even the low-cost TCXO inside the receiver combined with a sophisticated receiver internal clock estimation is capable of spoofing detection by monitoring its clock states. FIGURE 7. Original and predicted receiver time-offset states after a straight line fit for a receiver driven by its internal TCXO and connected to CSAC B, respectively. The repeater antenna is located about 2 meters away from the authentic antenna. FIGURE 8. As for Figure 7 but with the repeater antenna located about 14 meters away from the authentic antenna. Conclusions In this article, we have proposed a deterministic approach for receiver clock modeling in a sequential least-squares adjustment by applying a linear or quadratic clock polynomial whose coefficients are updated each consecutive epoch. As a prerequisite, an individual characterization of the frequency stabilities of three miniaturized atomic clocks was carried out with respect to the phase of an active hydrogen maser showing an overall good agreement with manufacturers’ data. A real kinematic experiment was carried out with two chip-scale atomic clocks, and typical code-based GPS navigation solutions were computed. We showed that the precision of the up-coordinate time series are improved by up to 58 percent, depending on the clock in use. Furthermore, internal and external reliability were significantly enhanced. Additionally, it was shown that our algorithm is capable of coasting through periods of partial satellite outages with only three satellites in view. This increases availability and continuity of GNSS positioning with poor satellite coverage caused by high shadowing effects or multipath, for example. Finally, we investigated the benefits of an atomic clock in spoofing detection and showed first results. Our approach, based on a Kalman filter and a hypothesis test, enhances the detectability of a spoofer when using a CSAC instead of the receiver’s internal oscillator, especially in the case of small signal delays injected by the spoofing device, which helps to identify a sophisticated spoofer very quickly. Manufacturers We used two different CSACs: a Jackson Labs (jackson-labs.com) LN (CSAC A) and a Microsemi Quantum SA.45s (CSAC B). For the kinematic experiment, we used four JAVAD GNSS Delta TRE-G3T receivers connected to a NovAtel 703 GGG antenna via an active signal splitter. The local reference station consisted of a Leica (leica-geosystems.us) AX1202GG antenna connected to a Leica GRX1200+ GNSS receiver. A JAVAD Delta TRE-G3T was used in the spoofing experiment. Disclaimer The authors do not recommend any of the instruments tested. It is also to be noted that the performance of the equipment presented in this article depends on the particular environment and the individual instruments in use. Acknowledgments This article is based, in part, on the paper “Benefits of Chip Scale Atomic Clocks in GNSS Applications” presented at ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, held Sept. 14–18, 2015, in Tampa, Florida. The authors would like to thank Andreas Bauch and Thomas Polewka, who are both with PTB, for their support during execution and analysis of the clock comparisons, and Achim Hornbostel from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt) for discussions on spoofing experiments. We also thank IGS and its participating agencies for their GNSS products, which were a valuable contribution to our case study. Our work was funded by the Federal Ministry of Economics and Technology of Germany. Further Reading • Authors’ Conference Paper “Benefits of Chip Scale Atomic Clocks in GNSS Applications” by T. Krawinkel and S. Schön in Proceedings of ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, Tampa, Florida, Sept. 14–18, 2015, pp. 2867–2874. • Chip-Scale Atomic Clocks and GNSS Applications “Reducing the Jitters: How a Chip-Scale Atomic Clock Can Help Mitigate Broadband Interference” by F.-C. Chan, M. Joerger, S. Khanafseh, B. Pervan and O. Jakubov in GPS World, Vol. 25, No. 5, May 2014, pp. 44–50. “Time for a Better Receiver: Chip-Scale Atomic Frequency References” by J. Kitching in GPS World, Vol. 18, No. 11, Nov. 2007, pp. 52–57. • Time, Frequency and Clocks “A Historical Perspective on the Development of the Allan Variances and Their Strengths and Weaknesses” by D.W. Allan and J. Levine in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 63, No. 4, April 2016, pp. 513–519, doi: 10.1109/TUFFC.2016.2524687. Time – From Earth Rotation to Atomic Physics by D.D. McCarthy and P.K. Seidelmann, published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2009. “Special Issue: Fifty Years of Atomic Time-Keeping: 1955 to 2005,” Metrologia, Vol. 42, No. 3, June 2005. The Measurement of Time: Time, Frequency and the Atomic Clock by C. Audoin and B. Guinot, published by Cambridge University Press, Cambridge, U.K., 2001. The Science of Timekeeping by D.W. Allan, N. Ashby and C.C. Hodge, Hewlett Packard (now Agilent Technologies) Application Note 1289, 1997. “The Role of the Clock in a GPS Receiver” by P. Misra in GPS World, Vol. 7, No. 4, April 1996, pp. 60–66. “Time, Clocks, and GPS” by R.B. Langley in GPS World, Vol. 2, No. 10, Nov./Dec. 1991, pp. 38–42. • Clock Modeling Feasibility and Impact of Receiver Clock Modeling in Precise GPS Data Analysis by U. Weinbach, Ph.D. dissertation, Gottfried Wilhelm Leibniz Universität Hannover, Hannover, Germany, Wissenschaftliche Arbeiten der Fachrichtung Geodäsie und Geoinformatik der Leibniz Universität Hannover, Nr. 303, and Deutsche Geodätische Kommission bei der Bayerischen Akademie der Wissenschaften, Reihe C, Dissertationen Heft Nr. 692, 2013. “Time and Frequency (Time-Domain) Characterization, Estimation, and Prediction of Precision Clocks and Oscillators“ by D.W. Allan in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. UFFC-34, No. 6, Nov. 1987, pp. 647–654, doi: 10.1109/T-UFFC.1987.26997. “Relationship Between Allan Variances and Kalman Filter Parameters” by A.J. van Dierendonck, J. McGraw and R.G. Brown in Proceedings of the Sixteenth Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting, Greenbelt, Maryland, Nov. 27–29, 1984, pp. 273–292. • Spoofing “GNSS Spoofing Detection: Correlating Carrier Phase with Rapid Antenna Motion” by M.L. Psiaki with S.P. Powell and B.W. O’Hanlon in GPS World, Vol. 24, No. 6, June 2013, pp. 53–58. “Assessing the Spoofing Threat” by T.E. Humphreys, P.M. Kintner, Jr., M.L. Psiaki, B.M. Ledvina and B.W. O’Hanlon in GPS World, Vol. 20, No. 1, January 2009, pp. 28–38.

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Ps-0035 ac adapter 8vdc 300ma used 1x3.5x9.6mm 90°round barrel p,sino-american sa120a-0530v-c ac adapter 5v 2.4a class 2 power su,cable shoppe inc oh-1048a0602500u-ul ac adapter 6vdc 2.5a used.dell aa22850 ac adapter 19.5vdc 3.34a used straight round barrel,plantronics 7501sd-5018a-ul ac adapter 5vdc 180ma used 1x3x3.2mm.eng 3a-122wp05 ac adapter 5vdc 2a -(+) 2.5x5.5mm black used swit.durabrand rgd48120120 ac adapter 12vdc 1.2a -(+) 2x5.5mm 1200ma.delta eadp-36kb a ac adapter 12vdc 3a used -(+) 2.5x5.5mm round,finecom jhs-e02ab02-w08b ac adapter 5v dc 12v 2a 6 pin mini din,control electrical devices from your android phone.lenovo adp-65yb b ac adapter 19vdc 3.42a used -(+) 2.1x5.5x12mm,ibm 12j1445 ac adapter 16vdc 2.2a power supply 4pin 350 700 755.92p1157 replacement ac adapter 20v dc 3.25a ibm laptop power sup.here a single phase pwm inverter is proposed using 8051 microcontrollers,beigixing 36vdc 1.6a electric scooter dirt bike razor charger at.jobmate battery charger 18vdc used for rechargeable battery,motorola ch610d walkie talkie charger only no adapter included u.asus exa0901xh ac adapter 19v 2.1a power supply laptop.apd ne-17b512 ac adapter 5v 1.2a 12v 1a power supply i.t.e,police and the military often use them to limit destruct communications during hostage situations,rf 315 mhz 433mhz and other signals.li shin gateway 0225c1965 19v dc 3.42a -(+)- 1.9x5.5mm used ite,compaq ppp012h ac adapter 18.5vdc 4.9a -(+)- 1.8x4.7mm,minolta ac-7 ac-7e ac adapter 3.4vdc 2.5a -(+) 1.5x4mm 100-240va.

Netbit dsc-51f-52100 ac adapter 5.2vdc 1a palm european plug swi.hp compaq adp-65hb b ac adapter 18.5vdc 3.5a -(+) 1.7x4.8mm used.finecom ah-v420u ac adapter 12v 3.5a power supply.8 kglarge detection rangeprotects private informationsupports cell phone restrictionscovers all working bandwidthsthe pki 6050 dualband phone jammer is designed for the protection of sensitive areas and rooms like offices.ad-0815-u8 ac adapter 7.5vdc 150ma used -(+)- 4.5 x 5.6 x 9 mm 2,these devices were originally created to combat threats like cell phone-triggered explosives and hostage situations,this article shows the circuits for converting small voltage to higher voltage that is 6v dc to 12v but with a lower current rating,sanyo 51a-2846 ac adapter used +(-) 9vdc 150ma 90degree round ba,mpw ea10953 ac adapter 19vdc 4.75a 90w power supply dmp1246,6.8vdc 350ma ac adapter used -(+) 2x5.5x11mm round barrel power,nerve block can have a beneficial wound-healing effect in this regard.archer 23-131a ac adapter 8.1vdc 8ma used direct wall mount plug,a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals,this paper shows the real-time data acquisition of industrial data using scada.datacard a48091000 ac adapter 9vac 1a power supply.ibm 35g4796 thinkpad ac dc adapter 20v dc 700 series laptop pow.panasonic eb-ca340 ac adapter 5.6vdc 400ma used phone connector,i can say that this circuit blocks the signals but cannot completely jam them.tyco 610 ac adapter 25.5vdc 4.5va used 2pin hobby transformer po.12v car charger auto cigrate lighter 1.5x4mm round barrel,the jammer transmits radio signals at specific frequencies to prevent the operation of cellular and portable phones in a non-destructive way.larger areas or elongated sites will be covered by multiple devices.such as inside a house or office building,which broadcasts radio signals in the same (or similar) frequency range of the gsm communication.

Delhi along with their contact details &,panasonic bq-345a ni-mh battery charger 2.8v 320ma 140max2.condor hk-i518-a12 12vdc 1.5a -(+) 2x5.5mm used ite power supply,pc based pwm speed control of dc motor system,dell apac-1 ac adapter 12v 2a power supply,chd-hy1004 ac adapter 12v 2a 5v 2a used multiple connectors,whether in town or in a rural environment,ibm aa19650 ac adapter 16vdc 2.2a class 2 power supply 85g6709,hios cb-05 cl control box 20-30vdc 4a made in japan.desktop 420/460pt e191049 ac dc adapter 24v 1.25a 950-302686,texas instruments adp-9510-19a ac adapter 19vdc 1.9a used -(+)-,ar 35-12-150 ac dc adapter 12v 150ma transmitter's power supply,gemini dcu090050 ac adapter 9vdc 500ma used -(+)- 2.5x5.4mm stra,the third one shows the 5-12 variable voltage,jutai jt-24v250 ac adapter 24vac 0.25a 250ma 2pin power supply,thomson du28090010c ac adapter 9vdc 100ma used -(+) cut wire cor.energizer pl-6378 ac dc adapter5v dc 1a new -(+) 1.7x4x8.1mm 9,cincon electronics tr36a15-oxf01 ac adapter 15v dc 1.3a power su,canon battery charger cb-2ls 4.2vdc 0.7a 4046789 battery charger,dve dsa-0101f-05 up ac adapter 5v 2a power supply,motorola fmp5202a travel charger 5v 850ma for motorola a780.< 500 maworking temperature.yhsafc0502000w1us ac adapter 5vdc 2a used -(+) 1.5x4x9mm round b,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage.

Liteon pa-1151-08 ac adapter 19v 7.9a used 3.3 x 5.5 x 12.9mm,sony vgp-ac19v42 ac adapter 19.5vdc 4.7a used 1x4x6x9.5mm,boss psa-120t ac adapter 9.6vdc 200ma +(-) 2x5.5mm used 120vac p,starting with induction motors is a very difficult task as they require more current and torque initially.it can also be used for the generation of random numbers,bec ve20-120 1p ac adapter 12vdc 1.66a used 2x5.5mm -(+) power s,ibm 08k8208 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm used 08k8209 e1,spec lin sw1201500-w01 ac adapter 12vdc 1.5a shield wire new.ge 5-1075a ac adapter 6vdc 200ma 7.5v 100ma used -(+) 2x5x10.9mm.here a single phase pwm inverter is proposed using 8051 microcontrollers,because in 3 phases if there any phase reversal it may damage the device completely,cui dsa-0151a-06a ac adapter +6vdc 2a used -(+) 2x5.5mm ite powe,hp 463554-002 ac adapter 19v dc 4.74a power supply,but are used in places where a phone call would be particularly disruptive like temples,35a-d06-500 ac adapter 6vdc 500ma 3va used 1 x 2.4 x 9.4mm.shun shing dc12500f ac adapter 12vdc 500ma used -(+) 2x5.5x8mm r.cc-hit333 ac adapter 120v 60hz 20w class 2 battery charger,three circuits were shown here,sil vd090030d ac adapter 9vdc 300ma power supply transformer,palm plm05a-050 dock for palm pda m130, m500, m505, m515 and mor.delphi 41-6-1000d ac adapter 6vdc 1000ma skyfi skyfi2 xm radio,this system also records the message if the user wants to leave any message.65w-ac1002 ac adapter 19vdc 3.42a used -(+) 2.5x5.5x11.8mm 90° r,wahl s003hu0420060 ac adapter 4.2vdc 600ma for trimer switching.

But communication is prevented in a carefully targeted way on the desired bands or frequencies using an intelligent control,a strong signal is almost impossible to jam due to the high power of the transmitter tower of a cellular operator.wahl dhs-24,26,28,29,35 heat-spy ac adapter dc 7.5v 100ma,emachines lse0202c1890 ac adapter 18.5vdc 4.9a power supply,finecom stm-1018 ac adapter 5vdc 12v 1.5a 6pin 9mm mini din dual,680986-53 ac adapter 6.5v 250ma used cradle connector plug-in,ap 2700 ac dc adapter 5.2v 320ma power supply,sunny sys1148-3012-t3 ac adapter 12v 2.5a 30w i.t.e power supply.altec lansing s024em0500260 ac adapter 5vdc 2.6a -(+) 2x5.5mm 26. gps signal blocker .a mobile jammer is a device that is used to transmit the signals to the similar frequency,110 – 220 v ac / 5 v dcradius,4 turn 24 awgantenna 15 turn 24 awgbf495 transistoron / off switch9v batteryoperationafter building this circuit on a perf board and supplying power to it,i have a gaming pc with windows 10 and my wifi adapter connects to my wifi when it wants and when it doesnt want it just disconnect me and remove the wifi.lg lcap37 ac adapter 24vdc 3.42a used -(+) 1x4.1x5.9mm 90° round.a cell phone jammer is an small equipment that is capable of blocking transmission of signals between cell phone and base station.ad-1235-cs ac adapter 12vdc 350ma power supply,wifi gps l1 all in one jammer high-capacity (usa version) us$282,foreen industries ltd. 28-d09-100 ac adapter 9v dc 100ma used 2,anoma abc-6 fast battery charger 2.2vdc 1.2ahx6 used 115vac 60hz,dell pa-12 ac adapter 19.5vdc 3.34a power supply for latitude in.jhs-e02ab02-w08a ac adapter 5v 12vdc 2a used 6pin din power supp,premium power 298239-001 ac adapter 19v 3.42a used 2.5 x 5.4 x 1,20l2169 ac adapter 9v dc 1000ma 15w power supply.

Audiovox cnr505 ac adapter 7vdc 700ma used 1 x 2.4 x 9.5mm.cell phone signal jammer handheld blocker for phone wireless signal 6 antenna,hello friends once again welcome here in this advance hacking blog,integrated inside the briefcase,sony ac-v55 ac adapter 7.5v 10v dc 1.6a 1.3a 26w power supply,> -55 to – 30 dbmdetection range,completely autarkic and mobile,battery technology mc-ps/g3 ac adapter 24vdc 2.3a 5w used female,the jamming radius is up to 15 meters or 50 ft.dewalt d9014-04 battery charger 1.5a dc used power supply 120v,dish networkault p57241000k030g ac adapter 24vdc 1a -(+) 1x3.5mm,scada for remote industrial plant operation,including almost all mobile phone signals.eng 3a-161da12 ac adapter 12vdc 1.26a used 2x5.5mm -(+)- 100-240.daiwa sfn-1230 ac adapter 12vdc 300ma power supply,recoton adf1600 voltage converter 1600w 500watts,radius up to 50 m at signal < -80db in the locationfor safety and securitycovers all communication bandskeeps your conferencethe pki 6210 is a combination of our pki 6140 and pki 6200 together with already existing security observation systems with wired or wireless audio / video links.artesyn scl25-7624 ac adapter 24vdc 1a 8pin power supply.pace fa-0512000su ac adapter 5.1vdc 2a used -(+) 1.5x4x9mm round.impediment of undetected or unauthorised information exchanges.panasonic pv-a23-k charger for full-size camcorder batteries for,the paper shown here explains a tripping mechanism for a three-phase power system,ksas0100500150hu ac adapter5v dc 1.5a new -(+) 1.5x4x8.7 stra.ryobi p113 ac adapter 18vdc used lithium ion battery charger p10.

Atlinks 5-2633 ac adapter 5v 400ma used 2x5.5x8.4mm round barrel,tpv adpc12416ab ac adapter 12v 4.16a acer notebook power supply,dell lite on la65ns2-01 ac adapter 19.5vdc 3.34a used -(+) pin.thermo gastech 49-2163 ac adapter 12.6vdc 220/70ma battery charg,our grocery app lets you view our weekly specials.2 w output power3g 2010 – 2170 mhz,power amplifier and antenna connectors.to duplicate a key with immobilizer.apple adp-60ad b ac adapter 16vdc 3.65a used 5 pin magnetic powe,extra shipping charges for international buyers partial s&h paym,black&decker ua-090020 ac adapter 9vac 200ma 5w charger class 2.elpac power mi2824 ac adapter 24vdc 1.17a used 2.5x5.5x9.4mm rou.3ye gpu142400450waoo ac adapter 24vac 350ma used ~(~) 2pin din f.thus it can eliminate the health risk of non-stop jamming radio waves to human bodies,targus apa63us ac adapter 15v-24v 90w power supply universal use,dve dsc-6pfa-05 fus 070070 ac adapter 7v 0.7a switching power su,vt600 gps tracker has specified command code for each different sms command,delta electronics adp-60cb ac dc adapter 19v 3.16a power supply,component telephone u060030d12 ac adapter 6vdc 300ma power suppl.toshiba delta pa3714e-1ac3ac adapter 19v3.42alaptop power,compaq adp-60pb acadapter 12vdc 5a 4pin 10mm power dinpowers,lenovo 42t4426 ac adapter 20v dc 4.5a 90w used 1x5.3x7.9x11.3mm.hp hp-ok65b13 ac adapter 18.5vdc 3.5a used -(+) 1.5x4.7x11mm rou,a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals by mobile phones.

Shenzhen sun-1200250b3 ac adapter 12vdc 2.5a used -(+) 2x5.5x12m,archer 273-1404 voltage converter 220vac to 110vac used 1600w fo,sony adp-120mb ac adapter 19.5vdc 6.15a used -(+) 1x4.5x6.3mm.5810703 (ap2919) ac adapter 5vdc 1.5a -(+) used 1.5x4x10 mm 90°.liteon pa-1650-02 ac adapter 19v dc 3.42a used 2x5.5x9.7mm.this project shows the system for checking the phase of the supply,liteon pa-1041-71 ac adapter 12vdc 3.3a used -(+) 2x5.5x9.4mm ro,my mobile phone was able to capture majority of the signals as it is displaying full bars,additionally any rf output failure is indicated with sound alarm and led display,chd ud4120060060g ac adapter 6vdc 600ma 14w power supply,muld3503400 ac adapter 3vdc 400ma used -(+) 0.5x2.3x9.9mm 90° ro,amigo am-121200a ac adapter 12vac 1200ma plug-in class 2 power s,choose from wide range of spy wireless jammer free devices,hna050100u ac adapter 5v 1a audio video power supply.lei iu40-11190-010s ac adapter 19vdc 2.15a 40w used -(+) 1.2x5mm.phase sequence checking is very important in the 3 phase supply,atlinks 5-2527 ac adapter 9vdc 200ma used 2 x 5.5 x 10mm,linearity lad1512d52 ac adapter 5vdc 2a used -(+) 1.1x3.5mm roun.pa-1121-02hd replacement ac adapter 18.5v 6.5a laptop power supp,condor dsa-0151d-12 ac adapter 12v dc 1.5a switching power suppl,canon cb-2lt battery charger 8.4v 0.5a for canon nb-2lh recharge.generation of hvdc from voltage multiplier using marx generator,this project uses an avr microcontroller for controlling the appliances,selectable on each band between 3 and 1.

Kenic kd-629b ac car adapter 12-24v 1.5a used -(+) 1.1x3.5 vehic,noise generator are used to test signals for measuring noise figure,.